1. Field of the Invention
This invention generally relates to a hub transmission for a bicycle. More specifically, the present invention relates to an internally geared bicycle hub transmission.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle drive train.
Internally mounted multi-speed hub transmissions are mounted to the rear wheel of a bicycle and allow a rider of the bicycle to select different gear ratios to change the pedaling force. Typically a hub transmission has a hub axle that is mounted to the bicycle frame. The hub axle rotatably supports a driver for transmitting a pedaling force to the hub transmission through a sprocket and a chain. The hub transmission further comprises a hub shell which is likewise rotatably supported by the hub axle.
The hub shell accommodates a power transmission mechanism which is disposed between the driver and the hub shell for transmitting rotational power from the driver to the hub shell. The power transmission mechanism provides a plurality of power transmission paths with different gear ratios that can be selected by using a shift mechanism, wherein each power transmission path typically produces a specific gear ratio. To establish the plurality of power transmission paths the power transmission mechanism ordinarily has several planetary gear mechanisms.
Current internal hub transmissions are designed to provide 10 or more speed stages. For example, one proposed internal hub transmission is disclosed in German Patent Publication No. DE 10 2004 011 052 A1. The hub transmission according to German Patent Publication No. DE 10 2004 011 052 A1 allows a selection between 9 speed stages which are provided by a plurality of planetary gear mechanisms. The known hub transmission has three planetary gear mechanisms that allow the combination of three speed stages with another five speed stages, for a total of nine speed stages with a gear ratio of 340%. The hub transmission includes a first planetary gear mechanism having a first sun gear that is non-rotatably mounted to the hub axle, a first planetary gear rotatably supported by a first planetary gear carrier and a first ring gear. The first planetary gears are disposed between the first sun gear and the first ring gear and mesh with the same.
A second planetary gear mechanism includes a second sun gear which is arranged on the first planetary gear carrier. Second planetary gears are mounted on the first ring gear. A third planetary gear mechanism is formed similar to the second planetary gear mechanism, and includes a third sun gear mounted on the first planetary gear carrier. The third sun gear meshes with third planetary gears with each being non-rotatably joined to the respective second planetary gears. Thereby a two-step planetary gear is formed. The third planetary gears mesh with a second ring gear to transmit the torque of the third planetary gear mechanism to the second planetary gear mechanism.
The shifting mechanism of this hub transmission comprises a pawl carrier which allows coupling the driver selectively with components of the respective planetary gear mechanisms to produce different gear ratios. To this end the pawl carrier comprises a plurality of controllable pawls, namely six pawls that are actuated by means of three shifting cams.
The arrangement of the two-step planetary gear on the first ring gear in combination with the second ring gear that meshes with the two-step planetary gears, leads to a pile type of internal hub transmission. Since the second ring gear overlaps the other components of the three planetary gear mechanisms, the diameter of the second ring gear and, thus, the diameter of the internal hub transmission is increased. Moreover, the pile type construction of the internal hub transmission leads to an increased total weight of the hub.
As described above, the second and third sun gears are each mounted on the first planetary gear carrier. Therefore, the second and third sun gears each rotate together with the first planetary gear carrier around the hub axle. In particular, the power transmission path for speed stages 8 and 9 comprises the driver, the sixth pawl and the first planetary gear carrier wherein the first planetary gears rotate around the first sun gear. The power transmission path further has the first ring gear, the second ring gear, the first pawl, the pawl connecting the power transmission with the hub shell and the hub shell. In speed stage 8, the third planetary gear rotates around the third sun gear and in speed stage 9 the second planetary gear rotates around the second sun gear.
Due to this differential rotational type of the planetary gear mechanism the power transmission paths are complicated. In particular the power transmission paths for speed stages 8 and 9 inefficiently transmit power.
A similar hub transmission is known from German Patent Publication No. DE 197 20 796 A1, which discloses a multiple speed hub having a plurality of planetary gear mechanisms arranged in series. The hub transmission disclosed therein enables either a 7 speed shifting or a 14 speed shifting. The 14 speed hub transmission comprises five planetary gear mechanisms, the components of which can be selectively locked to establish the desired power transmission paths. A first planetary gear mechanism comprises a first sun gear rotatably supported by a hub axle which can be locked with the same. The first sun gear meshes with the smaller diameter of a two-step planetary gear which is rotatably supported by a first planetary gear carrier. The first planetary gear carrier is non-rotatably connected with the hub shell. The large diameter of the two-step planetary gear meshes with a ring gear that can be locked either with the hub axle or the first sun gear. A second planetary gear mechanism comprises a second sun gear rotatably supported by and lockable with the hub axle. Second planetary gears mesh with the sun gear and a second ring gear wherein the second ring gear is non-rotatably connected with the first sun gear. A third planetary gear mechanism comprises a third sun gear which is rotatably supported by and lockable with the hub axle. Third planetary gears mesh with the third sun gears which are non-rotatably connected with the second planetary gears with the respective second planetary gears. The second sun gear meshes with the small diameter stage of the stepped planetary gears, and the third sun gear meshes with the large diameter stage of the stepped planetary gears.
The fourth and fifth planetary gear mechanisms are similar to the second and third planetary gear mechanisms and are symmetrically formed and arranged. The fourth and fifth planetary gear mechanisms therefore likewise comprise two-stage planetary gears, wherein the planetary gears of the second and third planetary gear mechanism and the planetary gears of the fourth and fifth planetary gear mechanisms are rotatably supported by means of a common planetary gear carrier. The small diameter stage of the stepped planetary gears of the fourth and fifth planetary gear mechanisms mesh with a ring gear that is non-rotatably connected with a driver.
A further embodiment of the 14-speed hub transmission is based on a modified embodiment of the above described hub transmission, and has a second ring gear which meshes with both small diameter stages of the symmetrically arranged stepped planetary gears. The common planetary gear carrier is replaced with two separate planetary gear carriers with the planetary gear carrier of the second and third planetary gear mechanisms being non-rotatably connected with the first sun gear. The planetary gear carrier of the fourth and fifth planetary gear mechanisms is non-rotatably connected with the driver.
Owing to the increased number of clutches required for locking the separate components of the planetary gear mechanisms, for example the ring gears with the sun gears, the hub transmission according to German Patent Publication No. DE 197 20 796 A1 is complicated and comparatively expensive.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle hub transmission. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.